1. Field of the Invention
The present invention relates to a four-unit type of zoom lens system lending itself well fit for still cameras, cinecameras or other cameras, esp., video cameras and, more specifically, to a compact zoom lens arrangement comprising a reduced number of lenses and having a variable power ratio of about 6-8.
2. Description of the Prior Art
In recent years, video cameras have been smaller in size and lower in price than ever before and, with this, zoom lenses for video cameras are now required to get ever smaller and ever more inexpensive.
In most cases, zoom lenses having a variable power ratio of 6 or more for video cameras, available so far in the art, are of a four-unit type built up of, in order from the object side, positive, negative, negative and positive lens units, with the overall lens length kept constant during zooming, the 2nd lens unit used for power variation and the 3rd lens unit intended for image position correction.
With demand for lens miniaturization in mind, however, some zoom lens systems for video cameras--which are variable in the overall lens length during zooming and are generally designed such that the overall lens length is minimized at the wide angle end have been proposed in JP-P-61(1986)-55653, JP-A-58(1983)-179809 and JP-A-60(1985)-14212.
However, these zoom lens systems each consist of as large as 13 to 15 lenses. For lens systems for cameras using small-sized image sensors, typically video cameras, the more the number of lenses used, the more difficult it is to assure a space large enough to accommodate such lenses, thus offering an obstacle to their miniaturization. This problem becomes more serious as the image sensors get smaller.